1. Field of the Invention
The present invention relates to an apparatus for driving an actuator of a camera module in a mobile device.
2. Description of the Related Art
A camera module in a mobile device, such as a smart phone, a tablet PC, and a camera has extendedly applied functions, such as an auto focus (AF) and an optical image stabilizer (hereinafter, referred to as an OIS) to obtain a high-definition image. Therefore, a linear current driving technology of an actuator, such as a voice coil motor (VCM) for low noise among core technologies for implementing the AF and OIS functions, has become increasingly important.
The VCM used to move a lens module in the AF and the OIS moves the lens module to a desired position by controlling the direction and amount of current flowing in a coil which is mounted outside a camera lens module.
U.S. Patent Publication No. 2012/0076343 describes a linear current driving of a VCM 3, in which the VCM includes a control circuit 11, a digital-to-analog converter 14, a driving circuit 15a including an operational amplifier 151 and an NMOS transistor 152, and a resistor R. The control circuit 11 outputs a digital code having any bit corresponding to a desired current value and the digital-to-analog converter 14 converts the digital code having any bit into an analog voltage. The analog voltage value converted by the digital-to-analog converter 14 is supplied to the resistor R through the driving circuit 15a and a driving current Ivcm flows through the NMOS transistor 152.
In this configuration, the resistor R needs to have a resistance value of approximately 0.5 to 1 ohm to obtain a driving current of 100 mA. However, the small resistance value is difficult to be accurately implemented within the actual IC and sensitively reacts to a temperature change and a process deviation, such that it is difficult to obtain stable performance.